The present invention relates to an optical network switch.
Current network systems use either electrical switching (like router or layer-2 switch) or optical point-to-point dedicated link for interconnection. FIG. 1A shows an example network, with 102.a through 102.f representing optical switch; 104.a through 104.d for router or layer-2 switch; 112.a through 112.h for optical WDM (wavelength division multiplexing) link, each representing a fiber with multiple wavelengths; and 114.a through 114.e for electrical connection. The interfaces on 102 that connects 104 are optical transponders that converts electrical signal into optical, with each transponder connects one wavelength. In traditional solution, if traffic from 104.b wants to reach 104.a, there is either a dedicated wavelength connecting 102.c and 102.a (FIG. 1B)), or an intermediate node, say 104.d, that can receive traffic from 104.b and send traffic to 104.a (FIG. 1C)). Electrical switching involves OEO conversion and electrical processing, which is both expensive and power hungry; dedicated optical point-to-point link requires significant number of transponders thus very high cost, in particular when link capacity is much larger than traffic demands.
Two known solutions are available for the aforementioned problem: one is OFDMA (Orthogonal Frequency Division Multiple Access), and the second is InTune Networks' sub-wavelength networking solution Optical Packet Switch & Transport (OPST).
OFDMA uses subcarrier multiplexing, for one transmitter to reach multiple receivers using the same wavelength, and for one receiver to receive different subcarriers from multiple wavelengths (thus multiple transmitters). All-optical switching (e.g. through wavelength selective switch, or WSS) if done in sub-wavelength level, for subcarriers to go from one transmitter to different receivers; each receiver receives multiple wavelengths that carry different subcarriers. This method has only a limited number of sharing capability and not very efficient in spectral usage because of the needs for guardband.
OPST method uses ring topology. Each port is treated as a node in a ring, and is able to access any other ports in the ring. Each receiver accepts a dedicated wavelength and works in burst mode; each transmitter has a tunable laser to put the inserted packet to the corresponding wavelength based on its header. The packet (or a burst of aggregated packets) is sent only when the particular wavelength is idle. The channel access technology is similar to CSMA (carrier sensing multiple access) which is used in traditional shared media Ethernet. The solution has several drawbacks: 1) application limited to ring topology; 2) limited maximum ring length; 3) tolerance of power fluctuations; 4) large number of carriers to sense; 5) larger latency; among others.